Insert molding is a precision manufacturing process that involves inserting a prefabricated component (such as a metal or plastic component) into a mold cavity, then injecting plastic material around it and forming the finished part through an injection molding machine. To obtain a final single component that combines the characteristics and functions of the insert and plastic material. Elimold has summarized some tips and issues that can be used during insert mold projects after years of service in insert injection molding.
Issues to consider for insert molding projects
Insert molding is to pre-embed (bury) metal inserts (metal terminals, contacts and other parts) into the cavity, and then perform injection molding after the mold is closed to produce injection molded products that wrap the metal inserts in resin. This process involves using two materials of different properties to produce related products, so there are many issues to consider when using this process for production. The following are the tips and issues summarized by Elimold for insert molds.
- Design considerations: The design of the insert should be compatible with the mold design and injection molding process. The insert should have appropriate draft angles, clearances, and surface finishes to facilitate insertion and removal from the mold. The position and orientation of the insert within the mold should also be considered to ensure proper flow of the molten material and minimize the risk of defects. It is also necessary to consider that the insert will not be scratched or damaged during the production process. These risks need to be avoided in each action of placing the insert into the mold, during the injection process, and removing it from the mold.
- Material selection: The material of the insert should be compatible with the plastic material used in the injection molding process. For plastic inserts, the thermal expansion coefficients and melting points of both materials should be similar to avoid warping or cracking of the finished part. If the insert is metal, this is not a concern. Many products we see in our daily lives have both metal and plastic, for example, different connectors for cars, computers or medical devices, etc., and many electronic housings with brass nuts or aluminum nuts to make the product stronger.
- Insert preparation: The insert should be clean and free of any contaminants or debris that may affect the bond between the insert and the plastic material. Some inserts may require pre-treatment, such as sandblasting or applying a bonding layer, to enhance the bonding performance. Elimold manufactures many metal insert products, some of which require electroplating, Cu+Ni+gold plating, such as automotive connectors. Some of them use Cu directly, and some use AL with Cu+Ni+silver plating for electric vehicles.
- Mold preparation: The mold should be designed and manufactured to accommodate the insert and ensure proper alignment and positioning. The mold should also have a sturdy clamping mechanism to hold the insert in place during the injection molding process. In most cases, many insert molds need to be manufactured with high precision to reduce the risk of future production, so it requires high-level equipment, high-speed CNC centers, mirror EDM, slow-feed wire cutting machines, etc., and CMM measurement machine support is also required to control the quality of the entire processing process.
- Injection molding process: The injection molding process should be optimized to ensure that the plastic material flows properly around the insert and minimize the risk of defects such as voids, dents, flash or warpage. Process parameters such as temperature, pressure and cooling time should be carefully monitored and adjusted to obtain consistent and high-quality parts.
Elimold Insert Mold Real Case Study
Elimold encountered an insert molding mold project for automotive connectors. The plastic material used in the product is PPA plus glass fiber. This material is hard and not easy to produce burrs. However, in addition to the insert problem, there are other greater problems encountered in the production and manufacturing of this mold.
The mold manufacturing process is basically the same as the usual insert mold: all pins are placed in the mold for injection molding to obtain a block with pins, and then the block is placed in the final mold to obtain the final product, which can reduce the thicker area and avoid dents.
However, we encountered more problems during the injection molding production process.
The first is that the pin scratches and damages the electroplated surface. According to the current situation, we designed a bakelite block to protect the pin, put it into the mold through the injection molding process, and remove it after the product comes out. Due to the injection molding pressure, a gap needs to be left to allow the pin to move a small distance while ensuring that no burrs are produced.
Another problem is that the pin is easy to oxidize, so we changed the electroplating process and strengthened quality control.
This is a challenging technical case. Therefore, we held several meetings to discuss and analyze the technology, process control and find solutions. The good news is that these measures helped and we completed and met the customer’s requirements.